Field
The present application relates to photonic waveguide structures.
Related Art
Waveguides are used in many applications to efficiently confine and guide electromagnetic radiation. Some waveguides are created using the principle of total internal reflection within a dielectric, or an approximation thereof. For example, in the field of integrated photonics, a first dielectric material of a first index of refraction is used to form a waveguide path and a dielectric of a second dielectric material, with a second index of refraction with a smaller value than the first index of refraction, is formed around the waveguide path. Using a dielectric material with a larger index as the waveguide path results in guiding the electromagnetic radiation down the waveguide path.
Silicon is conventionally used to create waveguides for wavelengths of light used in the telecommunications industry for at least two reasons. First, silicon has a low absorption coefficient (the imaginary part of the index of refraction) resulting in transparent waveguides at wavelengths used in telecommunications . Second, the real part of the index of refraction is high (n˜3.5), resulting in good confinement of the electromagnetic radiation within the waveguide. Thus, silicon waveguides designed for use at telecommunication wavelengths, in the region from 1260 nm to 1675 nm, can have small transverse dimensions relative to the wavelength of the confined electromagnetic radiation. For example, conventional silicon waveguides at telecommunications wavelengths may have transverse dimensions on the order of hundreds of nanometers.
A waveguide has several properties that determine the characteristics of the electromagnetic radiation that is guided by the waveguide. In particular, the transverse dimensions of the waveguide (e.g., the horizontal and vertical directions that are perpendicular to the direction of propagation of the light down the waveguide path) determine the mode structure of the guided radiation. For example, the number of modes that may be supported by the waveguide is determined by the transverse dimensions of the waveguide.